It has passed almost 40 years since gamma camera was first developed in Japan. This paper reviews the progress of the physics in nuclear medicine in Japan with emphases on instrumentation and quantification of radio-nuclide imaging. The topics include the progress of gamma camera, SPECT, PET and image reconstruction from projections. Various improvements are highlighted including new position arithmetic of gamma cameras, progress of spatial resolution of gamma cameras and PET scanners, analytical methods of attenuation correction in SPECT, move from 2D-PET scanners with septa to fully 3D-PET scanners, advance of the methods of image reconstruction for 3D-PET, efforts to speed up iterative image reconstruction algorithms, etc. Besides technical instrumentation, developments of key components such as scintillators, photosensors, etc. are also described.

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Since W. C. Roentgen discovered X-rays in 1895, screen-film systems have been used in diagnostic imaging for a long period. Appearance of digital systems has led to major changes in the diagnostics area. In this paper, I describe the following things such as analog and digital images, the purpose of the image evaluation, relationship between sensitivity and image quality of medical imaging, evaluation using the concept of signal-to-noise ratio (SNR), and computer aided diagnosis (CAD).

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